1. Technical Field
The present invention relates to an electronic device having a semiconductor device mounted to a wiring substrate and an electronic apparatus using the electronic device.
2. Related Art
Technologies for mounting electronic components such as semiconductor integrated circuits (ICs) are used for circuit boards and liquid crystal devices mounted to various types of electronic apparatuses. For example, an IC chip for driving liquid crystal is mounted as a semiconductor device on a liquid crystal display to drive the liquid crystal panel. The IC chip may be mounted directly on a glass substrate which constitutes the liquid crystal panel or on a flexible printed circuit (FPC) which is mounted on the liquid crystal panel. The glass substrate and the FPC are examples of a wiring substrate. The mounting structure of the former is called a chip-on-glass (COG) structure, and the mounting structure of the latter is called a chip-on-FPC (COF) structure.
In a process of mounting the IC chip that drives liquid crystal of the liquid crystal display having the COG structure, an IC chip 1021 is disposed above a glass substrate 1011, with reference to FIG. 12A. Interposed between the IC chip 1021 and the glass substrate 1011 is an anisotropic conductive film (ACF) 1222 containing conductive particles 1222a dispersed in a thermoset resin 1222b. Both the IC chip 1021 and the glass substrate 1011 are then heated and pressured, with the conductive particles 1222a therebetween, so as to bring bump electrodes 1021B, 1021B of the IC chip 1021 into an electrical contact state on the alignment sections of electrode terminals 1011bx, 1011dx on the glass substrate 1011. The contact state is to be maintained by the cured thermoset resin 1222b. 
Generally, in order to improve reliability of the conductive connection between the bump electrodes 1021B and the electrode terminals 1011bx, 1011dx, it is necessary to fix the relative position of the IC chip 1021 to the glass substrate 1011 in a state that the conductive particles 1222a between them are elastically deformed. This is because to maintain the state of electrical contact with the interposed conductive particles 1222a even if the thermoset resin 1222b is thermally expanded due to temperature changes.
However, it is extremely difficult to obtain a predetermined amount of elastic deformation of the conductive particles 1222a because of their minuteness.
Therefore, with reference to FIG. 12B, a technology for composing a bump electrode 1010 is proposed (e.g., see JP-A-2-272737), in which a resin protrusion 1012 is provided above an active surface of the IC chip 1021, and a conductive film 1020 is provided above the surface of this resin protrusion 1012. In this case, an insulating film 1026 is provided in advance on the surface of a pad 1024 of the IC chip 1021, and a portion of the insulating film 1026 is made to open so as to provide a coupling section 1022 to the pad 1024. Then, the conductive film 1020 of the bump electrode 1010 is extended to the coupling section 1022 so that the bump electrode 1010 performs as an electrode terminal of the IC chip 1201.
By pressing the bump electrode 1010 to a terminal of the glass substrate 1011, the resin protrusion 1012 constituting the bump electrode 1010 is elastically deformed. Because the resin protrusion 1012 constituting the bump electrode 1010 is sufficiently larger than the conductive particles 1222a contained in the ACF, a predetermined amount of elastic deformation can be obtained. In this state, the IC chip 1021 is fixed to the glass substrate 1011 using the thermoset resin 1222b, so that it becomes possible to maintain the electrical contact state brought by the interposed conductive particles 1222a even if the thermoset resin 1222b is thermally expanded due to temperature changes.
However, because the glass substrate 1011, resin protrusion 1012, conductive film 1020, and thermoset resin 1222b that constitute an electrical contact section made conductive by the bump electrode 1010 have different thermal expansion coefficients, the amount of deformation in each constituent by application of heat varies. Particularly, if the resin protrusion 1012 is convex-shaped, and if the conductive film 1020 is aligned in plurality on the surface of the resin protrusion 1012, the amount of deformation increases near end portions of the resin protrusion 1012 in a longitudinal direction due to the thermal expansion. With the increase in the deformation amount of the resin protrusion 1012, the variation in the deformation amount of each constituent increases, thereby possibly leading to deterioration of the electrical contact state and to conductive disconnection. In this case, the possibility of conductive disconnection between the IC chip 1021 and the glass substrate 1011 is a problem. Therefore, conductive connection that can withstand temperature changes is required, and this is a technology required for the electronic devices.